1. Field of Invention
The invention relates to a semiconductor device and a manufacturing method thereof and, in particular, to a semiconductor device and a manufacturing method thereof carried out by flip-chip bonding.
2. Related Art
In comparison with the conventional Si metal oxide semiconductor field effect transistor (Si MOSFET), GaN high electron mobility transistor (GaN HEMT) has a wider band gap, higher breakdown voltage and higher carrier mobility. Because having the above-mentioned features, the GaN HEMT can have a lower turn-on resistance under a faster switching rate. However, the GaN HEMT innately belongs to a depletion mode device, so a cascode transistor structure is proposed for the cooperation between the GaN HEMT and other enhancement mode electrode devices. FIG. 1 is a schematic circuit diagram of a cascode transistor 1. As shown in FIG. 1, the cascode transistor 1 is formed by the connection of a GaN HEMT 11 and a field effect transistor 12 (which can be a Si MOSFET for example). Besides, the GaN HEMT 11 and the field effect transistor are mostly connected together by wire bonding in the current technology. By making the field effect transistor 12 disposed at the gate of the cascode transistor 1, the cascode transistor 1 can become an enhancement mode electronic device also with the advantages that the GaN HEMT 11 has. The cascode transistor 1, like a normal field effect transistor, includes the source S, the gate G and the drain G.
However, when the GaN HEMT 11 and the field effect transistor 12 are connected by wire bonding, some problems will occur as follows. First, the additional connection wire will cause the additional parasitic inductance, and the additional parasitic inductance will limit the frequency response of the device so as to worsen the device characteristic. Second, if the cascode transistor 1 is formed by wire bonding, the field effect transistor 12 needs to be carried out by a planar structure, which costs more than a vertical structure. Third, in order to avoid the overlap between the drain of the GaN HEMT 11 and other electrodes, the thickness of the passivation layer of the GaN HEMT 11 needs to be increased, and therefore the manufacturing cost of the device is increased.